[Asterisk-Dev] Feature request: auto-guessing NAT status based on From: IP address

[John Todd]

[Sorry to put this up to the list instead of submitting code; I can't 
code my way out of a wet paper bag, as I've said before.]


Proposal:

Extension to the "nat=" flag in sip.conf to automatically guess on NAT status.

Reason:

I have a bunch of people that keep moving their SIP devices between 
home and work (NAT and non-NAT IP space) and I get tired of switching 
their "nat=" status every time they move.  Most (but of course, not 
all) NAT devices give out RFC1918 addresses, so in any given REGISTER 
or INVITE status we have a pretty good idea if a device is NAT'ed or 
not.  Why not use that data to solve the problem for the 90% of the 
people who have NATs that provide addresses in this space?  Retaining 
the "yes" and "no" flags maintains backwards static compatibility for 
those who need it or for address spaces that are NAT'ed but do not 
fall into the RFC1918 area.


Syntax:

Old syntax:
  nat=[1,0]

New Syntax
  nat=[1,0,yes,no,auto]

The "0" and "1" definitions will retain their historical meaning, and 
will also have duplicates with the terms "yes" and "no" to mean "1" 
and "0" respectively.

If the keyword "auto" is specified, the system will make a 'best 
guess' as to the status of the NAT flag for that SIP peer.  If the IP 
address in the "From:" field in an INVITE or REGISTER is set to one 
of the common RFC1918 addresses, then the system will assume "yes" 
and the appropriate re-write and "via" headers will be set.


Definitions:

RFC1918 space:

10/8
   - match on first octet being a "10"

172.16/12
  -  match on first octet being 172, and second octet being between 16 and 31

192.168/16
  - match on first octet being 192, and second octet being 168

See RFC1918 (http://www.zvon.org/tmRFC/RFC1918/Output/index.html)


JT